A bending structure previously used in an USB interface metal casing is gradually replaced by an integrated structure. However, in the prior art, a customer generally has a need for designing a fillet R at a port of an USB interface metal casing having an integrated structure. The fillet, especially the fillet at the port, is commonly formed by firstly forming a contour of the USB interface metal casing by stamping forming, then forming a port of the USB interface metal casing by punching process; the remaining portion is then used as the fillet. The manufacturing method has drawbacks that the processes are complicated, the shrinkage of the materials at the fillet is uneven, and additional processes such as burring or the like are needed to perform to the port after punching, and thus it is impossible to obtain the USB interface metal casing meeting the size requirements for one time.